The invention relates to a directional drilling system for cutting a bore in the earth, and particularly to an improved drilling platform and steering and guidance system for rock drilling.
It is known in the art of drilling earth and rock bores to utilize a drill string having a drilling tool attached to its outer end with a drill bit which is rotated by a positive displacement motor. A fluid such as air, slurry, or a relatively incompressible liquid is forced down the drill string and on passing through the fluid operated motor, causes rotation of a shaft connected to the drill bit. As the drilling tool progresses away from the drilling rig, more drill pipe is added between the drill bit motor and the drilling platform. As each joint of drill pipe is added to the drill string, the fluid flow to the drill bit motor must be interrupted. Once the connection of another joint of drill pipe is completed, the fluid flow to the drilling tool is again initiated. A typical fluid driven motor is illustrated in U.S. Pat. No. 4,936,397.
Numerous methods have been proposed for steering the drill string. A most typical steering apparatus and method includes the use of a bent sub. Typical bent sub type directional drilling devices are illustrated in U.S. Pat. Nos. 4,653,598; 4,905,774; and 2,329,597. A problem with the bent sub type directional drilling devices is that the bore cut by such devices is substantially oversized since the entire elbow rotates in the bore. For example, the prior bent sub type drilling devices may cut a bore from 2 to 10 inches oversized due to the angle of the bent sub.
Another component of the typical directional drilling system is a guidance system which measures the position of the drilling tool. A typical directional drilling system uses steering tools to survey the curved and horizontal portions of the tool while drilling. These wireline tools allow continuous reading of tool-face azimuth and inclination. The azimuth reading is measured with three magnetometers and the inclination is measured with three accelerometers. U.S. Pat. No. 4,905,774 discloses a device for guiding a drilling tool through geological formations.
Other methods are known for controlling the direction of small diameter earth drilling tools by using radio detection systems which monitor the position of the tool. However, these systems and methods require an individual to physically track the tool, limiting such systems to shallow bores. Such systems are not suitable for use when boring under streams, rivers, and other obstructions.
In addition to the bent sub directing devices, U.S. Pat. No. 3,243,001 discloses a rotary well drilling tool which controls the path of the drill. Control of the direction of the tool is brought about by a change in the position between a housing and a concentric sleeve wherein the position becomes eccentric. The changing of the position of the housing and respective sleeve requires a complicated fluid system working through various arrangements of orifices, conduits, pistons, and piston rods. Other steering devices using eccentric members are shown in U.S. Pat. Nos. 4,220,213 and 4,319,649.
Accordingly, an object of the invention is to provide an improved apparatus and method for directionally drilling an earthen bore, particularly rock, in a simple and accurate manner.
Another object of the invention is to provide a steering system for actively controlling the direction of a drilling head and bit which requires only a slight overcutting and eliminates large oversized bores of the bore.
Another object of the present invention is to provide an apparatus and method for accurately guiding a directional drilling tool along a desired bore direction and path.
Another object of the present invention is to provide an apparatus and method for accurately controlling the direction of a directional drilling tool which includes a fluid motor eccentrically mounted with respect to the drilling head and requires few moving parts in the drilling head for controlling the position of the eccentric and the direction of the tool.
Another object of the invention is to provide an apparatus and method for directional drilling an earthen bore which includes a guidance system for determining the horizontal and vertical angular positions of the drilling head in a simple and reliable manner.
Another object of the present invention is to provide a guidance system for a directional drilling apparatus and method wherein a single axis angular rate sensor is utilized in a manner which yields angular positions about two orthogonal axis in a simple and reliable manner.
Another object of the present invention is to provide a simple and reliable guidance system for a directional drilling head which is non-magnetic and which is not influenced by anything except the displacement of the drilling head and which accurately measures any horizontal and vertical deviations and distance travelled by the drilling head in a simple and reliable manner.
Another object of the invention is to provide a control system for controlling the path of a directional drilling head which includes an eccentrically mounted fluid motor and rotating drill bit, an angular rate sensor, and an encoder for instantaneously indicating the eccentric position of the drill bit, and the position of the drilling head in a simple and reliable manner whereby the drill string is steered by stopping of drill string rotation at a desired eccentric position and by starting drill string rotation once deviations are eliminated.
Another object of the invention is to provide a directional drilling system having a drilling platform cartridge which may be inserted in a rock pit to provide a form about which concrete may be filled in the pit to provide a stable drilling platform.
Another object of the invention is to provide a directional drilling apparatus and method having an improved drilling frame assembly which advances the drill string through the earth while drilling a bore and by which accurate control of the drilling direction and process may be had.
Another object of the invention is to provide a control system for a directional drilling tool wherein the distance from a starting point may be determined in a simple and reliable manner using accelerometers which accurately measure distance travelled.
Another object of the present invention is to provide apparatus for directional drilling an earthen bore which includes a drill bit which cuts an eccentric pattern by continuous rotation of a drill string which results in equal clearance around the drill head resulting in a straight bore with little overcut and wherein the apparatus may be steered by stopping and starting rotation of the drill string to accurately control the direction of the drilling head and bit in a simple and reliable manner.
Another object of the invention is to provide a directional drilling system which is completely self contained and can be used at any depth and to bore under streams, rivers, and any other type of obstruction.